In recent years, as a window glass for a vehicle such as an automobile and a window glass for a building material to be attached to a building construction such as a house or a building, demands for a transparent resin plate are increasing instead of a conventional inorganic glass plate. Particularly, for a vehicle such as an automobile, for weight saving, use of a transparent resin plate as a window material has been proposed, and especially, an aromatic polycarbonate transparent resin plate is excellent in fracture resistance, transparency, light weight properties, easy processability, etc., and its use has been studied as a promising window material for a vehicle. Further, demands for such a transparent resin plate are expanding also for budding materials such as roofs of public facilities, or translucent sound barriers for balconies, carports, arcades or highways. However, such a transparent resin plate has had problems with respect to the abrasion resistance or weather resistance when it is used in place of a glass plate. Therefore, it has been proposed to form a coating film on the surface of a transparent resin plate by means of various hard coating agents, particularly silicone type hard coating agents, for the purpose of improving the abrasion resistance and weather-resistance of the transparent resin plate.
As an example of such a proposal, Patent Document 1 discloses a technique wherein an inorganic layer is formed on a polymer substrate for resin glass, and an alkoxysilane-containing hard coating layer is formed via such an inorganic layer. Further, Patent Document 2 discloses a technology of a coating composition which contains an organo polysiloxane resin having (meth)acrylic functional substituents and silanol groups.
Each of them is a technique relating to a silicone type hard coating layer which is capable of imparting the abrasion resistance and weather resistance as formed on a transparent resin plate, but the technique of Patent Document 1 is one to improve the adhesion of the hard coating layer, and the technique of Patent Document 2 is to improve the storage stability (weather resistance) as a coating composition, i. e. they are not ones to improve the abrasion resistance and weather resistance of the silicone type hard coating layer, for which further improvement of the performance is required.
On the other hand, in the case of the above transparent resin plate for building materials, applications are also increasing in which the resin plate is forcibly bent at ordinary temperature by so-called cold forming and is used in a bent state (hereinafter referred to as “use in a bent state”). Also in such applications, it is required to show an excellent property of the hard coating layer such as the solvent resistance, chemical resistance, etc., and the above mentioned further improvement of the performance is desired. In addition, use of a resin substrate having a silicone type hard coating layer having abrasion resistance and weather resistance to some extent, has been studied. However, the resin substrate having a silicone type hard coating layer has had problems such that it has no resistance against forcible bending at ordinary temperature, and due to cracking of the hard coating layer or formation of gathering of fine cracks (crazing) in the resin substrate, it lacks in transparency and is likely to undergo delamination of the hard coating layer or deterioration of the mechanical strength.
In order to use the resin substrate having a silicone type hard coating layer having weather-resistance in an application in a bent state or as a three dimensionally processed product, it is necessary to apply such a coating on a preliminarily bent resin substrate or to use a thermoformable resin substrate having a silicone type hard coating layer, but the hard coating layer itself is very sensitive to a thermal-stress and a bending stress, and cracks are likely to form after cooling a formed product to ordinary temperature, in many cases.
In order to solve such problems, Patent Document 3 discloses a technique for flexible silicone coating for a plastic substrate and for a process for producing a thermoformable abrasion resistant thermoplastic product, but there is no specific disclosure relating to forcible bending.
Therefore, it has been desired to develop a resin substrate having a silicone type hard coating layer which is capable of imparting sufficient abrasion resistance and weather resistance to a transparent resin substrate made of a polycarbonate type resin expected to be useful as various window materials or window materials for vehicles and which is capable of maintaining its excellent properties such as the transparency and fracture resistance for a long period of time, and further a resin substrate having a silicone type hard coating layer which can be used in a bent state and which has, in addition to the abrasion resistance and weather resistance, the cracking resistance when exposed to a mechanical stress.